Regenerative fuel pumps have been used in fuel delivery system for internal combustion engines due to their low cost, small size, and quiet operation. The regenerative fuel pump may be submerged in a fuel tank so the fuel pump can deliver sufficiently pressurized fuel to downstream components. For various reasons, the temperature of the fuel delivered to the regenerative pump may increase during operation of the engine. Due to the temperature rise fuel vapor bubbles may develop in the pump, reducing the pump flowrate, thereby decreasing the capacity and efficiency of the pump. In some cases, the flow may be decreased to the point where it may cause degradation in performance or cause the engine to stop. To address this issue, regenerative pumps may include a purge orifice allowing fuel vapor to be separated from the liquid fuel to thereby maintain pump efficiency.
Various types of purge orifices have been developed to decrease the amount of fuel vapor in the fuel. In particular the diameter of the purge orifice may be increased and the location of the purge orifice may be varied. In one approach, the purge orifice may be located further downstream of the pump inlet. One example is described in U.S. Pat. No. 5,284,417.
The inventors herein have recognized that during high flow conditions, increasing the size of the purge orifice and locating the purge orifice further downstream of the inlet may not increase the amount of fuel vapor that can be purged from the pump. Furthermore, when the size of the purge orifice is increased during high flow applications, the turbulence (i.e. flow interruption) in the pump may be increased as well, thereby decreasing pump efficiency. Thus, there may be a trade-off between an increased purge orifice size and/or orifice location to enable increased vapor separation on one hand, and the amount of flow interruption caused by the orifice on the other hand.
To address this apparent paradox, in one embodiment a rotodynamic (regenerative turbine) fuel pump in an internal combustion engine is provided. The rotodynamic fuel pump comprising a pump inlet extending through the lower housing allowing fuel to be drawn into the impeller chamber, a purge orifice including a purge inlet, a purge outlet, and a purge channel, extending through the lower pump housing allowing fuel vapor to be drawn out of the impeller chamber, and a purge outlet angle less than 90 degrees formed by the vertical flow direction through the purge outlet and the vertical plane defined by the side portion of the impeller.
In this way, it is possible to increase the vapor purging ability and limit the amount of flow interruption caused by the purge orifice without requiring substantial increases in the diameter of the purge orifice and/or movement of the purge orifice further downstream of the inlet. However, such actions may be taken in addition, if desired.